Development of vascular substitutes for low-flow peripheral bypass grafting - a review.

The development of a low-flow vascular prosthesis is a very topical issue. The authors present a pathway for the development of a prosthesis with optimal properties based on the idea of mimicking the characteristics of a biological model (saphenous vein graft) and programming these properties in the model of the prosthetic substitute. The vascular prosthesis presented consists of three layers - a non-absorbable scaffold representing vascular “media”, and two absorbable collagen layers - pseudointima and pseudoadventitia. The basic methods of physical testing are presented - the single axis stretch test and inflation-extension test, as well as other procedures that affect the final properties. These include collagen curing, antithrombotic treatment of the inner layer and the use of sterilization methods. The designed new graft was successfully implanted in an ovine model.

Comparing the hemodynamic effect of a large arteriovenous fistula during high and low cardiac output states.

Background: A large arteriovenous fistula (AVF) is a low-resistant circuit that affects organ perfusion and systemic hemodynamics even in standard conditions. The extent of its' effect in critical states has not been elucidated yet. We used norepinephrine to create systemic vasoconstriction, dobutamine to create high cardiac output, and rapid right ventricle pacing as a model of acute heart failure in a porcine model of high-flow AVF circulation. Methods: The protocol was performed on nine domestic female pigs under general anesthesia. AVF was created by connecting two high-diameter ECMO cannulas inserted in the femoral artery and vein. Continuous hemodynamic monitoring was performed throughout the protocol. Three interventions were performed-moderate dose of norepinephrine (0.25 ug/kg/min), moderate dose of dobutamine (10 ug/kg/min) and rapid right ventricle pacing to simulate low cardiac output state with mean arterial pressure under 60 mmHg. Measurements were taken with opened and closed arteriovenous fistula. Results: Continuous infusion of norepinephrine with opened AVF significantly increased mean arterial pressure (+20%) and total cardiac output (CO) (+36%), but vascular resistance remained virtually unchanged. AVF flow (Qa) rise correlated with mean arterial pressure increase (+20%; R = 0.97, p = 0.0001). Effective cardiac output increased, leading to insignificant improvement in organ perfusion. Dobutamine substantially increased cardiac output with insignificant effect on AVF flow and mean arterial pressure. Carotid artery blood flow increased significantly after dobutamine infusion by approximately 30%, coronary flow velocity increased significantly only in closed AVF state. The effective cardiac output using the heart failure model leading to decrease of carotid artery flow and worsening of brain and peripheral tissue oximetry. AVF blood flow also dropped significantly and proportionally to pressure, but Qa/CO ratio did not change. Therefore, the effective cardiac output decreased. Conclusion: In abovementioned extreme hemodynamic conditions the AVF flow was always directly proportional to systemic perfusion pressure. The ratio of shunt flow to cardiac output depended on systemic vascular resistance. These experiments highlight the detrimental role of a large AVF in these critical conditions' models.

A large arteriovenous fistula steals a considerable part of systemic blood flow during veno-arterial extracorporeal circulation support in a porcine model.

Background: Veno-arterial extracorporeal membrane oxygenation (V-A ECMO) is one of the most frequently used mechanical circulatory support devices. Distribution of extracorporeal membrane oxygenation flow depends (similarly as the cardiac output distribution) on regional vascular resistance. Arteriovenous fistulas (AVFs), used frequently as hemodialysis access, represent a low-resistant circuit which steals part of the systemic perfusion. We tested the hypothesis that the presence of a large Arteriovenous fistulas significantly changes organ perfusion during a partial and a full Veno-arterial extracorporeal membrane oxygenation support. Methods: The protocol was performed on domestic female pigs held under general anesthesia. Cannulas for Veno-arterial extracorporeal membrane oxygenation were inserted into femoral artery and vein. The Arteriovenous fistulas was created using another two high-diameter extracorporeal membrane oxygenation cannulas inserted in the contralateral femoral artery and vein. Catheters, flow probes, flow wires and other sensors were placed for continuous monitoring of haemodynamics and organ perfusion. A stepwise increase in extracorporeal membrane oxygenation flow was considered under beating heart and ventricular fibrillation (VF) with closed and opened Arteriovenous fistulas. Results: Opening of a large Arteriovenous fistulas (blood flow ranging from 1.1 to 2.2 L/min) resulted in decrease of effective systemic blood flow by 17%-30% (p < 0.01 for all steps). This led to a significant decrease of carotid artery flow (ranging from 13% to 25% after Arteriovenous fistulas opening) following VF and under partial extracorporeal membrane oxygenation support. Cerebral tissue oxygenation measured by near infrared spectroscopy also decreased significantly in all steps. These changes occurred even with maintained perfusion pressure. Changes in coronary artery flow were driven by changes in the native cardiac output. Conclusion: A large arteriovenous fistula can completely counteract Veno-arterial extracorporeal membrane oxygenation support unless maximal extracorporeal membrane oxygenation flow is applied. Cerebral blood flow and oxygenation are mainly compromised by the effect of the Arteriovenous fistulas. These effects could influence brain function in patients with Arteriovenous fistulas on Veno-arterial extracorporeal membrane oxygenation.

Is there circadian variation in cortisol levels in young sows in heart catheterization?

Cortisol is the main glucocorticoid (GC) hormone in pigs associated with stress response. It is well known that GCs levels are not stable during the day; their concentration is a circadian variable with the peak in the morning and the nadir in the night (in diurnal animals). Circadian variation is present during postnatal ontogeny. The onset of the circadian fluctuation occurs in pigs at the age of 3 to 20 weeks (according to the literature). The aim of our pilot study was to determine if young sows (used in cardiosurgical experiments) already developed the circadian variation. Twelve-week-old sows were used in the heart catheterization experiment. Cortisol was measured during four different stages of the experiment at two different times of the day (the operation was performed in the morning or afternoon). To determine circadian variation the Mann-Whitney test was used; to determine changes in cortisol levels within the experiment the Friedman test was performed. We didn't find any circadian variation (p>0.05) or statistical significant variation in the Friedman test (p>0.05). We assumed that our pigs are too young to have circadian rhythm present. Our findings are in accordance with many authors.

Analysis of the electrical heart field.

There are three basic procedures used for an assessment of the electrical heart field from the body surface: standard electrocardiography, vectorcardiography, and body surface potential mapping (BSPM). BSPM has two major advantages over both other methods: 1) it allows exploring the entire chest surface, thus providing all the information on the cardiac electric field available at the body surface; 2) it is more sensitive in detecting local electrical events, such as local conduction disturbances or regional heterogeneities of ventricular recovery. Nevertheless the results obtained using BSPM procedure cannot answer all questions about real causality of detected changes of the electrical heart field. We tried therefore to use mathematical model of the electrical field in order to answer these questions. A simple and anatomical forward calculation model was used to test the hypothesis whether the altered position of the heart could explain heterogeneity of repolarization at late stages of pregnancy in humans. The hypothesis was declined. Further findings included: A. Repolarization duration (represented by QT interval) in healthy subjects are distributed regularly and predictably on the body surface carrying no information about local pathology. B. At any systemic analysis of ventricular repolarization, it is vital to consider the regions where any electrode systems record low amplitudes due to methodological, not pathological reasons. C. Anatomical (heterogeneous) model did not yield superior results over simple (homogenous) ones possibly since none reflected the specific torso geometry of individual patients.

ECG body surface mapping changes in type 1 diabetic patients with and without autonomic neuropathy.

ECG body surface mapping (BSM) parameters in patients with diabetes mellitus Type 1 (DM1) are significantly different comparing to healthy non-diabetic subjects. Hypothesis that these changes are more pronounced in DM1 patients with autonomic neuropathy (AN) was tested. The parameters of BSM were registered by diagnostic system Cardiag 112.2 in 54 DM1 patients including 25 with AN and 30 control subjects. AN was diagnosed according to Ewing criteria when two or more Ewing tests were abnormal. In classic 12-lead ECG the heart rate was increased, QRS and QT shortened (p<0.01) and QT(C) prolonged in DM1 patients. The VCG measurement of QRS-STT angles and spatial QRS-STT angle showed non-significant differences. The absolute values of maximum and minimum in depolarization and repolarization isopotential, isointegral, isoarea maps were significantly different in DM1 patients in comparison with controls (p<0.01). The changes were more pronounced in DM1 patients with AN than in DM patients without AN (p<0.05). The QT duration measured in 82 leads of thorax was significantly shortened in 68 leads of both groups of DM 1 patients (p<0.01) when compared with controls. In 34 of them this shortening was more pronounced in DM1 patients with AN than in DM1 patients without AN (p<0.05). The results showed that the method of ECG BSM is capable to confirm the presence of autonomic neuropathy in diabetic patients.

Hemodynamic response to thoracoscopy and thoracotomy.

Operations in the pleural cavity are connected with circulatory changes in pulmonary circulation and general changes of hemodynamics. These changes are influenced by the position of patient's body on the operation table and by the introduction of artificial pneumothorax. Thoracoscopy is an advanced surgical approach in thoracic surgery, but its hemodynamic effect is still not known. The aim of the present study was to compare the hemodynamic response to surgeries carried out by open (thoracotomy - TT) and closed (thoracoscopy - TS) surgical approach. Thirty-eight patients have been monitored throughout the operation--from the introduction of anesthesia to completing the surgery. Monitored parameters were systolic blood pressure (BPs), diastolic blood pressure (BPd), O2 saturation (SaO2), systolic blood pressure in pulmonary artery (BPPAs), diastolic blood pressure in pulmonary artery (BPPAd), wedge pressure (P(W)), central venous pressure in right atrium (CVP), cardiac output (CO) and total peripheral resistance (TPR). No significant difference has been found in hemodynamic response between TT and TS groups. Significant changes of hemodynamic parameters occurring during the whole surgical procedure were detected in both technical approaches. The most prominent changes were found after the position of patients was changed to the hip position (significantly decreased BPs, BPd, MAP, SaO2 and BPPAs) and 5 min after the pneumothorax was established (restoration of the cardiac output to the initial value and significant decrease of the TPR). It can be concluded that the thoracoscopy causes almost identical hemodynamic changes like the thoracotomy.

Increasing Veno-Arterial Extracorporeal Membrane Oxygenation Flow Reduces Electrical Impedance of the Lung Regions in Porcine Acute Heart Failure.

Veno-arterial extracorporeal membrane oxygenation (VA ECMO) is a technique used in patients with severe heart failure. The aim of this study was to evaluate its effects on left ventricular afterload and fluid accumulation in lungs with electrical impedance tomography (EIT). In eight swine, incremental increases of extracorporeal blood flow (EBF) were applied before and after the induction of ischemic heart failure. Hemodynamic parameters were continuously recorded and computational analysis of EIT was used to determine lung fluid accumulation. With an increase in EBF from 1 to 4 l/min in acute heart failure the associated increase of arterial pressure (raised by 44%) was accompanied with significant decrease of electrical impedance of lung regions. Increasing EBF in healthy circulation did not cause lung impedance changes. Our findings indicate that in severe heart failure EIT may reflect fluid accumulation in lungs due to increasing EBF.

Electrode movement prevention - an animal model.

Electrode migration is the most common complication of spinal cord stimulation (SCS). The problem of longitudinal migration has already been solved, but lateral migration remains the most common current complication. The present article describes new electrodes fixation opportunities for the reduction of lateral migration in SCS. The pig was chosen as an animal model to illustrate a new protocol of electrode fixation for the control of lateral and longitudinal migration. The displacement of the electrode was measured using two different optical methods: the digital image stereo-correlation and the digital image processing methods. Fixation with two anchors has always considerably reduced electrode displacement and when fixation is done with two anchors and a loop then lateral migration is reduced by 62.5 % and longitudinal migration is reduced by 94.1 %. It was shown that the results are significantly different at the alpha=0.001 significance level. Based on a statistical evaluation it is possible to state that the differences between experimental results obtained for three different protocols of lead fixation are statistically significant and we can recommend the new fixation method for common practice.

The influence of purification of carp collagen used in a novel composite graft with sandwich construction of the wall on its biological properties and graft patency rates.

We compared graft outcome between two types of a novel composite three-layer carp-collagen-coated vascular graft in low-flow conditions in a sheep model. Collagen in group A underwent more cycles of purification than in group B in order to increase the ratio between collagen and residual fat. The grafts were implanted end-to-side in both carotid arteries in sheep (14 grafts in 7 sheep in group A, 18 grafts in 9 sheep in group B) and artificially stenosed on the right side. The flow in the grafts in group A decreased from 297±118 ml/min to 158±159 ml/min (p=0.041) after placement of the artificial stenosis in group A, and from 330±164ml/min to 97±29 ml/min (p=0.0052) in group B (p=0.27 between the groups). From the five surviving animals in group A, both grafts occluded in one animal 3 and 14 days after implantation. In group B, from the six surviving animals, only one graft on the left side remained patent (p=0.0017). Histology showed degradation of the intimal layer in the center with endothelization from the periphery in group A and formation of thick fibrous intimal layer in group B. We conclude that the ratio between collagen and lipid content in the novel three-layer graft plays a critical role in its patency and structural changes in vivo.

Natural remodeling of the distal anastomosis of an above-knee femoropopliteal bypass depicted by CT angiography of lower limbs improves geometry of the reconstruction.

The geometry of the distal anastomosis of a femoropopliteal bypass influences local hemodynamics and formation of intimal hyperplasia. We hypothesized that the distal anastomosis of an above-knee femoropopliteal bypass undergoes remodeling that results in displacement of the original course of the popliteal artery and change in the anastomosis angle. We identified 43 CT angiography examination with proximal femoropopliteal bypass and either a preserved contralateral popliteal artery or previous CTA before construction of the bypass for comparison. In these examinations, we measured the displacement distance and angle at the level of the distal anastomosis and compared these measurements with clinical and imaging data. The displacement distance was 8.8+/-4.9 mm (P<0.0001) and the displacement angle was -1° (IQR=44°). The angle between the inflow and outflow artery was 153+/-16° (P<0.0001). There was a negative association between the displacement angle and the angle between the bypass and the outflow artery (r=-0.318, P=0.037). Patients with reversed venous grafts had a greater displacement of the anastomosis (14.7+/-3.0 mm) than patients with prosthetic grafts (8.0+/-4.5 mm, P=0.0011). We conclude that construction of a distal anastomosis of proximal femoropopliteal bypass results in displacement of the original course of the popliteal artery towards the bypass and this effect is more pronounced in reversed venous grafts.

Severe acute heart failure - experimental model with very low mortality.

The growth in the experimental research of facilities to support extracorporeal circulation requires the further development of models of acute heart failure that can be well controlled and reproduced. Two types of acute heart failure were examined in domestic pigs (Sus scrofa domestica): a hypoxic model (n=5) with continuous perfusion of the left coronary artery by hypoxic deoxygenated blood and ischemic model (n=9) with proximal closure of the left coronary artery and controlled hypoperfusion behind the closure. The aim was a severe, stable heart pump failure defined by hemodynamic parameters changes: a) decrease in cardiac output by at least 50 %; b) decrease in mixed venous blood saturation to under 60 %; c) left ventricular ejection fraction below 25 %; and d) decrease in flow via the carotid arteries at least 50 %. Acute heart failure developed in the first group in one animal with no acute mortality and in the second group in 8 animals with no acute mortality. In the case of ischemic model the cardiac output fell from 6.70+/-0.89 l/min to 2.89+/-0.75 l/min. The saturation of the mixed venous blood decreased from 83+/-2 % to 58+/-8 %. The left ventricular ejection fraction decreased from 50+/-8 % to 19+/-2 %. The flow via the carotid arteries decreased from 337+/-78 ml/min to 136+/-59 ml/min (P

ECG body surface mapping (BSM) in type 1 diabetic patients.

Diabetes mellitus is a risk factor of cardiovascular diseases. ECG of patients with diabetes mellitus type 1 (DM 1) shows tachycardia (block of parasympathetic innervation) and abnormal repolarization (increased QT interval and QT dispersion (QTd)) indicating a risk of ventricular tachycardia and sudden death in young people with DM 1. The aim of the present report was to measure 145 parameters of the heart electric field in 22 patients (14 men, 8 women) with DM 1 without complications (mean age 32.8+/-11.4 years) and in 22 controls (11 men, 11 women, mean age 30.1+/-3.4 years). The duration of diabetes was 13.9+/-7.8 years. The parameters were registered by the diagnostic system Cardiag 112.2 and statistically evaluated by the Student and Mann-Whitney test. Tachycardia (86.3+/-2.7 beats.min(-1)), shortening of both QRS (79.9+/-1.6 ms) and QT (349.0+/-5.9 ms) and increased QT dispersion (115+/-36 ms) were observed in DM 1 when compared with the controls (75.0+/-2.1 beats. min.(-1), QRS 89.9+/-2.7 ms, QT 374.0+/-4.4 ms, QTd 34.0+/-12.0 ms, p<0.01). The QTc was 415.2+/-4.1 ms in DM 1 and 401.4+/-6.6 ms in controls (NS). Other significant findings in DM 1 were: higher maximum of depolarization isopotential maps (DIPMmax) in the initial phase of QRS and less positive in the terminal phase, more negative minimum (DIPMmin) during QRS similarly as the minimum in depolarization isointegral maps (DIIMmin) and the minimum in isointegral map of the Q wave (Q-IIMmin), lower maximum in repolarization isopotential maps (RIPMmax) and less negative minimum (RIPMmin), more negative amplitude of Q wave (Q-IPMAM) and more pronounced spread of depolarization (activation time). Our results confirmed a decreased parasympathetic to sympathetic tone ratio (tachycardia, shortening of the activation time) and revealed different depolarization and repolarization patterns in DM 1. The differences in heart electric field parameters measured by the BSPM method in DM 1 and in the controls indicate the importance of ECG examination of diabetic patients type 1 in the prevention of cardiovascular diseases.

Detection of microembolic signals in the common carotid artery using Doppler sonography in the porcine model of acute heart failure treated by veno-arterial extracorporeal membrane oxygenation.

Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is a method used for the treatment most severe cases of decompensated heart failure. The purpose of this study was to evaluate the risk of the formation of microembolisms during VA-ECMO-based therapy. Heart failure was induced with simultaneous detection of microembolisms and the measurement of blood flow rate in the common carotid artery (CCA) without VA-ECMO (0 l/min) and at the VA-ECMO blood flow rate of 1, 2, 3 and 4 l/min. If embolisms for VA-ECMO 0 l/min and the individual regimes for VA-ECMO 1, 2, 3, 4 l/min are compared, a higher VA-ECMO flow rate is accompanied by a higher number of microembolisms. The final microembolism value at 16 min was for the VA-ECMO flow rate of 0 l/min 0.0 (0, 1), VA-ECMO l/min 7.5 (4, 19), VA-ECMO 2 l/min 12.5 (4, 26), VA-ECMO 3 l/min, 21.0 (18, 57) and VA-ECMO 4 l/min, 27.5 (21, 64). Such a comparison is statistically significant if VA-ECMO 0 vs. 4 l/min p<0.0001, 0 vs. 3 l/min p<0.01 and 1 vs. 4 l/min p<0.01 are compared. The results confirm that high VA-ECMO flow rates pose a risk with regards to the formation of a significantly higher number of microemboli in the blood circulation and that an increase in blood flow rates in the CCA corresponds to changes in the VA-ECMO flow rates.

Electrocardiographic outcome of resynchronization therapy.

Cardiac resynchronization therapy (CRT) has proven efficacious in reducing or even eliminating cardiac dyssynchrony and thus improving heart failure symptoms. However, quantification of mechanical dyssynchrony is still difficult and identification of CRT candidates is currently based just on the morphology and width of the QRS complex. As standard 12-lead ECG brings only limited information about the pattern of ventricular activation, we aimed to study changes produced by different pacing modes on the body surface potential maps (BSPM). Total of 12 CRT recipients with symptomatic heart failure (NYHA II-IV), sinus rhythm and QRS width >/=120 ms and 12 healthy controls were studied. Mapping system Biosemi (123 unipolar electrodes) was used for BSPM acquisition. Maximum QRS duration, longest and shortest activation times (ATmax and ATmin) and dispersion of QT interval (QTd) were measured and/or calculated during spontaneous rhythm, single-site right- and left-ventricular pacing and biventricular pacing with ECHO-optimized AV delay. Moreover we studied the impact of CRT on the locations of the early and late activated regions of the heart. The average values during the spontaneous rhythm in the group of patients with dyssynchrony (QRS 140.5+/-10.6 ms, ATmax 128.1+/-10.1 ms, ATmin 31.8+/-6.7 ms and QTd 104.3+/-24.7 ms) significantly differed from those measured in the control group (QRS 93.0+/-10.0 ms, ATmax 79.1+/-3.2 ms, ATmin 24.4+/-1.6 ms and QTd 43.6+/-10.7 ms). Right ventricular pacing (RVP) improved significantly only ATmax [111.2+/-10.6 ms (p<0.05)] but no other measured parameters. Left ventricular pacing (LVP) succeeded in improvement of all parameters [QRS 105.1+/-8.0 ms (p<0.01), ATmax 103.7+/-7.1 ms (p<0.01), ATmin 20.2+/-3.7 ms (p<0.01) and QTd 52.0+/-9.4 ms (p<0.01)]. Biventricular pacing (BVP) showed also a beneficial effect in all parameters [QRS 121.3+/-8.9 ms (p<0.05), ATmax 114.3+/-8.2 ms (p<0.05), ATmin 22.0+/-4.1 ms (p<0.01) and QTd 49.8+/-10.0 ms (p<0.01)]. Our results proved beneficial outcome of LVP and BVP in evaluated parameters (what seems to be important particularly in the case of activation times) and revealed a complete return of activation times to normal distribution when using these CRT modalities.

A novel experimental model of acute respiratory distress syndrome in pig.

Acute respiratory distress syndrome (ARDS) is severe medical condition occurring in critically ill patients and with mortality of 33-52 % is one of the leading causes of death in critically ill patients. To better understand pathophysiology of ARDS and to verify novel therapeutical approaches a reliable animal model is needed. Therefore we have developed modified lavage model of ARDS in the pig. After premedication (ketamine and midazolam) 35 healthy pigs were anesthetized (propofol, midazolam, morphin, pipecuronium) and orotracheally intubated and ventilated. Primary ARDS was induced by repeated cycles of lung lavage with a detergent Triton X100 diluted in saline (0.03 %) heated to 37 °C preceded by pre-oxygenation with 100 % O(2). Single cycle included two subsequent lavages followed by detergent suction. Each cycle was followed by hemodynamic and ventilation stabilization for approx. 15 min, with eventual administration of vasopressors according to an arterial blood pressure. The lavage procedure was repeated until the paO(2)/FiO(2) index after stabilization remained below 100 at PEEP 5 cm H(2)O. In 33 pigs we have achieved the desired degree of severe ARDS (PaO(2)/FiO(2)<100). Typical number of lavages was 2-3 (min. 1, max. 5). Hemodynamic tolerance and the need for vasopressors were strongly individual. In remaining two animals an unmanageable hypotension developed. For other subjects the experimental ARDS stability was good and allowed reliable measurement for more than 10 h. The present model of the ARDS is clinically relevant and thus it is suitable for further research of the pathophysiology and management of this serious medical condition.

The ratio of diameters between the target artery and the bypass modifies hemodynamic parameters related to intimal hyperplasia in the distal end-to-side anastomosis.

Hemodynamics in the distal end-to-side anastomosis is related to early development of intimal hyperplasia and bypass failure. In this study we investigated the effect of diameter ratios between the target artery and the bypass at three different angles of the connection. The pulsatile flow field was visualized using particle image velocimetry in transparent models with three different angles of the connection (25°, 45°, 60°) and the diameter ratio between the bypass and the target artery was 4.6 mm : 6 mm, 6 mm : 6 mm, and 7.5 mm : 6 mm. Six parameters including location and oscillation of the stagnation point, local energy dissipation, wall shear stress (WSS), oscillatory shear index, spatial and temporal gradient of WSS and their distribution in the target artery were calculated from the flow field. In the wider bypass, the stagnation point oscillated in a greater range and was located more proximal to the anastomosis. Energy dissipation was minimal in a wider bypass with a more acute angle. The maximum WSS values were tree times greater in a narrow bypass and concentrated in a smaller circular region at the floor of the anastomosis. The oscillatory shear index increased with wider bypass and more acute angle. The maximum of spatial gradient of WSS concentrated around the floor and toe of the anastomosis and decreased with more acute angle and wider bypass, the temporal gradient of WSS was stretched more towards the side wall. Greater bypass to target vessel ratio and more acute anastomosis angle promote hemodynamics known to reduce formation of intimal hyperplasia.

The influence of the anastomosis angle on the hemodynamics in the distal anastomosis in the infrainguinal bypass: an in vitro study.

The geometric shape of the distal anastomosis in an infrainguinal bypass has an influence on its durability. In this article, we compared three different angles of the anastomosis with regard to the hemodynamics. Three experimental models of the distal infrainguinal anastomosis with angles of 25°, 45°, and 60° respectively were constructed according to the similarity theory to assess flow in the anastomoses using particle image velocimetry and computational fluid dynamics. In the toe, heel, and floor of the anastomosis that correspond to the locations worst affected by intimal hyperplasia, adverse blood flow and wall shear stress were observed in the 45° and 60° models. In the 25° model, laminar blood flow was apparent more peripherally from the anastomosis. In conclusions, decreasing the distal anastomosis angle in a femoropopliteal bypass results in more favorable hemodynamics including the flow pattern and wall shear stress in locations susceptible to intimal hyperplasia.

Novel porcine model of acute severe cardiogenic shock developed by upper-body hypoxia.

Despite the urgent need for experimental research in the field of acute heart failure and, particularly cardiogenic shock, currently there are only limited options in large animal models enabling research using devices applied to human subjects. The majority of available models are either associated with an unacceptably high rate of acute mortality or are incapable of developing sufficient severity of acute heart failure. The objective of our research was to develop a novel large animal model of acute severe cardiogenic shock. Advanced left ventricular dysfunction was induced by global myocardial hypoxia by perfusing the upper body (including coronary arteries) with deoxygenated venous blood. The model was tested in 12 pigs: cardiogenic shock with signs of tissue hypoxia developed in all animals with no acute mortality. Cardiac output decreased from a mean (+/- SD) of 6.61+/-1.14 l/min to 2.75+/-0.63 l/min, stroke volume from 79.7+/-9.8 ml to 25.3+/-7.8 ml and left ventricular ejection fraction from 61.2+/-4.3 % to 17.7+/-4.8 % (P

Regional tissue oximetry reflects changes in arterial flow in porcine chronic heart failure treated with venoarterial extracorporeal membrane oxygenation.

Venoarterial extracorporeal membrane oxygenation (VA ECMO) is widely used in treatment of decompensated heart failure. Our aim was to investigate its effects on regional perfusion and tissue oxygenation with respect to extracorporeal blood flow (EBF). In five swine, decompensated low-output chronic heart failure was induced by long-term rapid ventricular pacing. Subsequently, VA ECMO was introduced and left ventricular (LV) volume, aortic blood pressure, regional arterial flow and tissue oxygenation were continuously recorded at different levels of EBF. With increasing EBF from minimal to 5 l/min, mean arterial pressure increased from 47+/-22 to 84+/-12 mm Hg (P<0.001) and arterial blood flow increased in carotid artery from 211+/-72 to 479+/-58 ml/min (P<0.01) and in subclavian artery from 103+/-49 to 296+/-54 ml/min (P<0.001). Corresponding brain and brachial tissue oxygenation increased promptly from 57+/-6 to 74+/-3 % and from 37+/-6 to 77+/-6 %, respectively (both P<0.01). Presented results confirm that VA ECMO is a capable form of heart support. Regional arterial flow and tissue oxygenation suggest that partial circulatory support may be sufficient to supply brain and peripheral tissue by oxygen.